The present invention relates to a ball electrode forming method, and more particularly to a technology effectively applied to a semiconductor apparatus mounted on a wiring board or the like through the ball electrode.
Following high performance and miniaturization of electronic devices achieved in recent years, multiple pins and light, thin and short forms are required of semiconductor apparatus used for such electronic devices.
In response to such a tendency, as described in a well-known patent document (Japanese Patent Application Laid-Open No. 212021/1995), there has been presented a semiconductor apparatus of a so-called ball grid array (BGA) structure where external terminals corresponding to electrode pads of semiconductor devices are arranged in a matrix.
In the semiconductor apparatus that employs the BGA structure, for example, very small solder balls having diameters of about 0.5 to 0.7 mm are arranged in an array to be apart from one another at predetermined intervals, which function as external electrodes. Thus, many external electrodes are densely disposed on one surface of the semiconductor apparatus, consequently providing a package which enables transfer of many signals between the outside and the semiconductor devices.
An example of a method for forming a ball electrode in the conventional semiconductor apparatus of the BGA structure will be described below.
First, a semiconductor apparatus is prepared, which has a plurality of electrode pads electrically connected to semiconductor devices formed on the surface of a semiconductor substrate.
Subsequently, on the surface of the semiconductor apparatus where the electrode pads are disposed, a flux is applied to remove oxide films formed on the surfaces of the electrode pads and the solder balls.
Then, a mask having a plurality of openings is arranged on the flux-applied surface of the semiconductor apparatus. At this time, a corresponding flux-applied electrode pad is exposed from each of the plurality of openings formed on the mask.
After the mask is arranged in a predetermined position on the surface of the semiconductor apparatus, the solder balls are arranged in the openings formed in the mask. The solder ball arranged in each opening is fixed on the flux of the electrode pad exposed from the opening of the mask, and electrically connected to the electrode pad to form a ball electrode.